Electronic – Simulating a DC motor with a constant friction torque

dcloadmotorsimulinktorque

I'm trying to simulate a DC motor with simulink. The problem is that I don't know how to take a load torque into account. If the DC motor drives a wheel with constant velocity, there will be a constant frictional force working against the DC motor. How would this be implemented in a DC-motor simulink simulation?

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I have tried subtracting a load torque in between the two transferfunction blocks but then the simulated motor speed is always goes negative.

Best Answer

Your block Kt/(R+Ls) is torque. V/(R+Ls) is your current. Kt is torque per amp (Nm/A). You simply add a value after Kt/(R+Ls), if it's constant. Unfortunately, many loads are speed or position dependent and then it get's much more complicated (math wise). Model-wise it's pretty easy.